Process of envelopment



1 19, 1963 M. N. MUNIIZ -ETAL 3,077,649

PROCESS OF ENVELOPMENT Filed Jan. 19, 1960 v 2 Sheets-Sheet 1 N 3 INVEN TOKS MARio N. MuNiZ- AUGUST) C, C CAVALCANT] Feb..l9, 1963 M. N. MUNIZ ETAL 3,077,649

PROCESS OF ENVELOPMENT Filed Jan. 19, 1960 2 Sheets-Sheet 2 v \liiliiiliiliiilii \Ys INVENTORS MARio N- umz uwsro c. c. 0,4 v LcAuTi United States Patent 3,077,649 PROCESS OF ENVELOPMENT Mario Neuhaus Muniz, Rua Maragogi 89, and Augusto Cezar Caldas Cavalcanti, Avenida Copacabana 698, Ap. 701, both of Rio de Janeiro, Brazil Filed Jan. 19, 1960, Ser. No. 3,353 Claims priority, application Brazil Nov. 4, 1959 6 Claims. (Cl. 22-202) The process of envelopment according to the present invention relates to a new method of fixing the passing insulators to the metal parts supporting them, and consists in making said supports directly over the insulators, enveloping them by the die casting process whereby the insulators themselves act as male cores or inserts inside the dies. This process is destined specifically for the manufacture of ignition spark plugs for automobiles, scooters, generating groups, etc. and cheapens production decidedly.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings, wherein like reference characters indicate like parts throughout the several figures and in which:

FIG. 1 is an elevational view of a conventional spark plug shown partly in longitudinal section;

FIG. 2 is an elevation of the same spark plug without the shell;

FIG. 3 is an elevation of the shell alone, for the spark plug of FIG. 1, shown partly in section and including an end view;

FIG. 4 is an elevation of a complete spark plug made in accordance with the present invention;

FIG. 5 is an elevation partly in section of the spark plug of FIG. 4 omitting the central electrode, and

FIG. 6 is a central section of a die set in which the plug insulator is used as a core for casting the outer shell thereabout.

The conventional process for fabricating ignition plugs consists in fabricating the plug in two main parts and later joining them to form the assembly.

The first part of the conventional spark plug, referring to FIGS. l-3, comprises the insulator 6, having tapers 8, 9 at one end, with the central electrode 11 and the terminal 7 already placed and cemented to its place. The second part is the shell, a metal piece 1 which supports the insulator and contains the hexagonal part 2, the thread 3 for adaptation to the motor and 4 the mass ground electrode. The shell is made of soft steel or iron, entirely worked, inside and outside. It is fabricated in automatic lathes parting from hexagonal bars previously drawn out. As it is a hollow piece, the loss of material is enormous and the manufacturers have thus been forced to use the cheapest possible material. The mass electrode 4 shown in end view at 5, FIG. 3, is a piece of rectangular profile nickel alloy wire, welded from the end, electrically, to the top of the shell so as to be thereupon turned when the plug is ready. The junction is achieved by placing the insulator inside the shell supported by two copper joints 12. As the insulator does not fit precisely to the shell because the manufacture of ceramics requires an allowance of more or less .007 in all dimensions, there is a centering operation by an appropriate machine and thereupon a press of large tonnage turns the collar 13 of the shell over the upper joint. There is still another operation consisting in electrically heating the shell while under pressure of the press, in order to mold it better, and chiefly to count with the effort of the contraction resulting from the cooling process so as to guarantee the tightening and insulation of the assembly. The steel or iron shells require a chemical or galvanoplastic treatment against rust.

Thanks to the instant invention or process of envelopment illustrated in FIGS. 4-6, the fabrication of ignition spark plugs is highly simplified as the entire series of shell production operations and the junctions, or the closure, is reduced to one single operation, which is the operation of casting the shell around the insulator, by injection, in forms (dies) of steel, and from which process it comes out practically finished, with all the details, hexagonal, body, thread, marking, etc., perfectly adjusted to the insulator, counting also with the effort of contraction by the cooling process in order to contribute to the tightening.

There is no loss of material because only the material required to form the piece enters the die.

By the process of envelopment the insulator 16 is placed inside the die 15 supported on a small iron tube 20 which centers it and forms the space around the point. This little tube is fabricated by stamping and can be withdrawn or stay as part of the plug. The system of the cold die and rapid injection at high pressure is used, which is the chief basis for success of the modern technique of die casting.

The insulators for ignition plugs at present produced are made of sintered aluminium oxide, heated at 1600 to 1700 C. The part staying outside the plug is enameled at 800 C. They have exceptional qualities of dielectric power, mechanical resistance and, above all, resistance to the thermal shock.

In the process of envelopment the insulators are not affected by heat because they are placed within the dies entirely cold (like the dies). As the injection of the fusion alloy is extremely rapid, the die itself immediately starts withdrawing heat from the already solidified piece and immediately thereupon the opening of the die and the jet of water complete the cooling. The dies have a space for placing a piece of nickel wire of rectangular section 21 in order that the plug come out already with the mass electrode tightly held by the casting process. The insulators, designed and calculated especially for this object, must contain two or three grooves 17 on the body for better adherence of the metal. The ends will be designed in form, length, section, conicity, etc. for each model or type as the thermic values of the plugs are determined by means of the form of the ends and the space between them and the shell, and also by considering the thermic conductibility of the type of porcelain used, the plugs being adapted to the different types of motors and kinds of services. Hence, thanks to the process of envelopment, one can fabricate in the same set of equal dies various types of plugs, varying only the insulators, whereas, based on the actual system, to each type of insulator corresponds one type of a different shell. FIGURE 6 shows the insulator placed inside the die. One can see the thread 19, the space to be filled by the metal 18, the location of the mass electrode, and an adjustable end member 26 to hold the insulator in place under pressure of the molten metal. In FIG. 5 is shown a section of the plug as it comes out of the die, still without the central electrode. FIG. 4 shows a plug entirely completed with the central electrode assembled. In these figures, 22 is the uncovered portion of the insulator, 23 is the bore, and 25 is the cast shell partially covering the insulator. We do not indicate more details regarding the die, the method of opening, the system of ejection, injection channels, air exit, etc., as it would lead too far to describe the multiple modern dies which make 20 or 30 units with each injection; also because this belongs to the modern technique of die casting and has nothing to do with the object of this specification. The process of envelopment will use alloys of a relatively low fusion point, preferably alloys on the basis of aluminium, zinc and tin, although the modern die casting processes do not exclude the possibility of employing ferrous alloys. It is not absolutely necessary that the shells of the ignition spark plugs be of iron or soft steel. Up to the present day the question of price, of useability, of cutting speed, etc. has prevailed and had its influence. The shell of an aluminium alloywill do perfectly well and will not be affected by the heat question, or the question of corrosion by the combustion chemistry, considering that the modern motors have aluminium cylinder heads and for quite some time pistons of aluminium are likewise employed. The explosion chamber of the motors is formed by the top of the piston and by the head, both of aluminium. There will, accordingly, be no inconvenience in making the plug out of aluminium. On the aluminium heads the threads of the openings to fix the plugs are tapered in the aluminium itself. When placing a steel plug (even the best steel) the resistance to internal presure would continue to depend on the thread in the aluminium, which has a resistance for about times that effort. In case of an iron head and an aluminium plug, the positions are only inverted. The S.A.E. (Society of Automotive Engineers) nowadays gives us an appreciable number of alloys of high property on the basis of aluminium, all of them catalogued, with all characteristics and properties well defined, making possible thus the use of different alloys for different types of plugs.

We claim:

1. The method of making a spark plug which com prises fabricating a tubular insulator having a central bore and tapered end, placing said insulator in a mold to form the core thereof completely spaced from the mold and supported at the tapered end of the insulator by means of a metal sleeve, positioning a metal strip adjacent said sleeve with an end portion supported in a notch of the mold, casting a metal shell about said insulator, support sleeve and metal strip, removing the insulator and cast shell from the mold, inserting a central electrode through the bore of the insulator, and turning said end portion of the metal strip toward the central electrode to form a ground electrode.

2. The method of making a spark plug which comprises the steps of fabricating a tubular insulator having a bore for a central electrode and a tapered end, seating A, the tapered end of the insulator in a thin, bondable, metal sleeve shaped to form the chamber desired to surround the central electrode in the finished spark plug and which chamber determines the thermal character istics of the finished spark plug, placing said insulator in a mold to form the core thereof supported at one end solely by said sleeve and completely spaced from the walls of the mold, applying molten metal to the insulator and sleeve within the mold, and causing said metal to harden and form the shell of the spark plug directly bonded to said insulator and sleeve.

3. The method of making a spark plug according to claim 2 wherein said molten metal applied to the insulator and sleeve is forced into the mold under pressure.

4. The method of making a spark plug according to claim 3 wherein said mold is water cooled to quickly cool and contract the molten metal about the insulator and its supporting sleeve.

5. The method of making a spark plug according to claim 3 wherein a metal strip destined to become the end of the insulator opposite to said tapered end when the insulator is positioned in the mold as a core whereby to assist said sleeve in supporting the insulator centrally of the die and to seal the upper part of the insulator from the molten metal.

6. The method of making a spark plug according to claim 3 wherein a metal strip destined to become the ground electrode of the spark plug is placed in a notch in the mold with a portion extending next to said sleeve, whereby upon application of the molten metal the cast shell bonds said metal strip to said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 1,347,367 Gerband July 20,1920 1,362,773 Brewster Dec. 21, 1920 1,552,274 Champion Sept. 1, 1925 1,723,026 Ford Aug. 6, 1929 1,905,600 Nowosielski Apr. 25, 1933 2,015,482 Lilienfeld Sept. 24, 1935 2,307,403 Haas Jan. 5, 1943 2,400,917 Corbin May 28, 1946 2,446,908 Corbin Aug. 10, 1948 2,449,403 -McDougal Sept. 14, 1948 OTHER REFERENCES Die Casting, 1st ed., H. H. Doehler, published by McGraw-Hill Co., New York, 1951 (page relied upon). 

1. THE METHOD OF MAKING A SPARK PLUG WHICH COMPRISES FABRICATING A TUBULAR INSULATOR HAVING A CENTRAL BORE AND TAPERED END, PLACING SAID INSULATOR IN A MOLD TO FORM THE CORE THEREOF COMPLETELY SPACED FROM THE MOLD AND SUPPORTED AT THE TAPERED END OF THE INSULATOR BY MEANS OF A METAL SLEEVE, POSITIONING A METAL STRIP ADJACENT SAID SLEEVE WITH AN END PORTION SUPPORTED IN A NOTCH OF THE MOLD, CASTING A METAL SHELL ABOUT SAID INSULATOR, SUPPORT SLEEVE AND METAL STRIP, REMOVING THE INSULATOR AND CAST SHELL FROM THE MOLD, INSERTING A CENTRAL ELECTRODE THROUGH THE BORE OF THE INSULATOR, AND TURNING SAID END PORTION OF THE METAL STRIP TOWARD THE CENTRAL ELECTRODE TO FORM A GROUND ELECTRODE. 